In many telephone systems, a metering pulse indicative of a predetermined monetary value is sent from a local exchange (LE) over a landline (e.g., an electrical or fiber-optic cable) to the telephone which initiates the call to allow a user to monitor the cost of the call as it progresses. The rate at which the LE transmits the metering pulses varies depending on the rate per minute of the call. For a local call, the metering pulses may be spaced several minutes apart (e.g., three minutes) since the cost per minute is relatively inexpensive, whereas, for a more expensive long distance call, the metering pulses may be separated by only several seconds. These pulses are typically either 12 KHz or 16 KHz audio tones each lasting between 120-180 milliseconds, and in general, the rate of the metering pulses is constant once a call has been initiated.
Metering pulses are widely used in village public telephones (VPTs) which include public pay telephones and small businesses that provide telephone services. In localities where not every home has a telephone, these small businesses (referred to hereinafter as public call offices or PCOs) are quite popular. PCOs include processing equipment which counts the metering pulses received during a call and calculates the price of the call based upon the number of metering pulses received during the call. In some cases the current cost of the call is displayed to the user during the call. Once the call is completed the customer pays the operator of the PCO. Public pay telephones on the other hand require the user to pay in advance, and when the amount deposited by the user has been used, the user deposits additional money to continue the call.
Wireless (e.g., cellular) PCOs also exist for use in remote locations where wireline telephone service does not exist. However, a problem with current wireless communication is that the bandwidth of a wireless communication channel (i.e., the forward voice channel) is less than the bandwidth of a wireline channel. That is, frequencies outside the 300-3,000 Hz band are heavily attenuated, thus the 12 or 16 KHz metering pulse frequency will not be allowed to pass through to the PCO unit. Bandshifting the metering pulses to a lower frequency has proven to be impractical since the bandshifted signal is within the passband of the voice or data on the forward voice channel and thus is audible to the user. Filtering the bandshifted signal from the passband is impractical since it reduces the audio bandwidth, resulting in the loss of some speech information or data transmitted on the wireless channel.
Because of these problems, current wireless public pay telephone and PCOs generate their own metering pulses based on locally administered rate tables, which are neither synchronized nor tied to the metering pulses issued by the LE. Consider, for example, the wireless system disclosed in U.S. Pat. No. 5,361,297 which maintains a database of billing rate information for local and long distance telephone calls. The wireless pay telephone or PCO uses this billing rate information to generate its own local metering pulses once the outgoing call has been answered. A problem with this autonomous generation of the metering pulses is that each time the billing rates change for the LE, every wireless public pay telephone and PCO must have its internal billing rate information updated. This can lead to errors and it presents opportunities for billing rate changes to made by someone other than the authorized LE operator.
One approach for overcoming these problems is set forth in PCT application WO 95/20298 entitled "Method for Transmitting Tariff Data to a Subscriber Unit", published Jul. 27, 1995. This published application discloses accumulating metering pulses at a telecommunications network, and when the accumulated number of pulses exceeds a predetermined value, a lump sum value is transmitted from the telecommunication network via a radio signal to a subscriber unit. The transmission of the lump sum value to the subscriber units occurs regularly during the call and the transmission causes an interruption in the speech path (see pg. 3, lines 28-33). Hence, this approach is still problematic since it causes interference with the speech path, but does so less frequently in comparison to other prior art systems. Nonetheless, any interruption in the speech path inconveniences the parties' to a call and may cause the loss of data.
Therefore, there is a need for a wireless communication systems that is capable of providing metering pulse information from a LE to a wireless public call office without regularly interfering with the speech path.
An object of the present invention is to provide metering pulse information from a LE to a wireless PCO.